Al Stein

In a thread about a different plane ( Aerodynamics > Left rudder causes dive and right roll ), there's talk of adverse roll coupling in the 4-Star 40 (which I'd never seen mentioned before)...

Have you experienced anything like giving the 4-Star rudder and having it roll off into a dive??

Wonder

My Feedback: (7)

Hi Al,

I never had such an experience with my 4*40.

I use rudder for spins and snap-rolls.

It is capable of doing flat turns also, I have done these several times.

You turn the plane with the rudder and use opposite aileron to hold it level, then give it some up elevator to keep it from falling out of the sky.

The last time I flew this plane I lost the canopy in flight and haven't flown it since.

I ordered a new one from the dealer in Ebensburg. If it is in next week I'll be down to pick it up and visit my daughter in J-town. She is still there taking a summer class at UPJ.

Later,
Tim

RLDIII

My Feedback: (1)

Hi Al,
You ask about adverse roll coupling with rudder application in the 4* planes. Well, all I can comment on are my stock 4*40 and my clipped wing 4*60, but it has not been a problem with either, and I use a LOT of rudder input in both. Like the previous poster, I do a lot of snaps and spins (GREAT flat spins) and even tumbles with my 4*40. It even knife edges reasonably well, but then I have a lot of power on it (O.S. 70 FS Surpass). It may exibit a little PROVERSE roll coupling in knife edge, but I hesitate to say for sure because I tend to just add a little aileron in knife edge (if needed) without even thinking about it much.
On my 4*60, besides clipping one bay off of each wing tip, I also added about 30% more rudder area (it could use even more with my YS .91AC and 15 x 8 prop!). However, like with my 4*40, I left the stock wing dihedral alone. With the 4*60, this combo gives me one of my best knife edging monoplanes in my fleet.
I really suspect that some of these guys out there are opening up a can of worms when they eliminate the dihedral on these wings. Since the design is a low (not mid) wing design, I have seen some that DO exhibit ADVERSE roll coupling to rudder input when they are built with the wings flat. Could that have been the problem in the discussion you saw??

Lee

Al Stein

I suspect that a flat wing could be the cause... if there was really a cause at all.

The person who made the comment claimed the the 4*40 notorious for doing this -- which really surprised me because I'd never heard that complaint against the 4-Stars before. Under the microscope, even the term notorious addresses reputation rather than experience, so the issue may have just resulted from somebody hearing what someone else was told by his brother-in-law's friend, who ought to know about such things because he hears everything from...

Wonder

My Feedback: (7)

RLDIII,

You say your 4*40 knive edges reasonably well, with a lot of power.

I have an O.S. 46LA on mine. It will not hold altitude in a knive edge. Other than buy a bigger engine, is there anything else that might help, or am I just to under powered.

Thanks,
Tim

Spike

My Feedback: (1)

Mine will knife edge at 3/4 throttle with a .46FX and a 11x5 prop. It pulls towards the belly like crazy, but it does knife edge.

RLDIII

My Feedback: (1)

Wonder, the extra power sure does help, but also make sure you are not nose heavy. Additionally, if you are using a spongy rudder linkage, such as the plastic tube in tube type set-up, then much of your rudder authority may be lost in a flexed rod instead of a firmly deflected rudder. This can often be seen in a plane that will knife edge OK on one side (rod in tension), but will not do it worth a hoot on the other side (rod in compression...flexes). In my case, I use a well supported carbon push-rod on rudder.

Lee

Wonder

My Feedback: (7)

Spike,

Your FX is more powerfull than my LA, but if you are running 3/4 throttle I should have enough at full throttle. I am using an 11X6 prop and will try an 11X5 next time.

Lee,

I am using the plastic tube in tube rods, so I will try on the tension side next time as well.

...... ......

I am using 10% fule, don't remember what the rpms are but will check that also to see if I need to bump up to 15%.

Thanks to both for the tips,
Tim

Al Stein

I support my nyrods (or similar) every 3 inches or so... the kits usually catch them every 6 or 7, so I should be getting about 9 times the stiffness.

I have retrofitted planes for more stiffness... attach follower strings to the old rods, pull them out (which is obviously easier said than done... takes a little cutting and twisting, feed the guide strings if I forgot to pull some through while removing the old rods, bind and glue new rods (actually the same rods are fine if I didn't damage them) to some stiff spruce strip, use the guide strings to ghuide them into place, fasten in each end and add some supports if possible (often not practical, but that's why the spruce is there).

The retrofit could probably be improved, too, by using arrowshafts or even carbon fiber tubes for stiffeners instead of the spruce sticks. It's not painless, but sometimes it's better than having to refinish the plane or just not use it the way you'd like to.


BTW Tim, I saw Dick from Allegheny Hobbies (Ebensburg) the other day... he says to call before dropping in to the shop, but it sounds like he's mostly available. Feel free to give me a buzz if he gets your stuff or you're in town.

Rcpilot

My Feedback: (78)

I built my 4*40 like a fun fly plane.

It has an OS 61FX for power and a Macs pipe for that little extra UUMMPH. The pipe makes it run 600rpm faster.

I increased ALL the control surfaces by 50%. Needless to say, my rudder is HUGE.

I put the elevator and rudder servos in the tail, just like them TOC guys. I didn't have to add any balance weight with this setup.

The plane will hover at about 1/2 throttle and will do a climbing knife-edge, no problem. Soemtimes, on a good day, I can run figure-8 knife edges down the length of the runway and back.

I am using dual aileron servos as well.
It's not my favorite plane, but definetly in the top five in my fleet.

I do experience a little roll coupling, and the tendency to pull towards the belly in knife edge. But I suspect that is due to the extreme modifications I did to the plane.

Ballance is VERY tail heavy on my plane. I like em that way.